The quality of each component in the world's food chain depends to a large extent on the component immediately preceding it. All other conditions being equal, the extent of any person's intake of proteins, carbohydrates, minerals and other essential ingredients will similarly depend upon the respective content of these items in the food consumed by any particular person. In turn, and viewing animal food sources as a particular example, the quality of the animal protein available for human intake will likewise depend to a large extent on the quality of protein made available to animals intended for human consumption. Because animals are generally fed whole grains, grain products, minerals and meals made from animal by-products, the quality of protein in any particular animal will likewise depend on the quality of protein available from these various animals foodstuffs.
As set forth in the preceding paragraph, one source of animal food is feed meal made from animal by-products. Animal by-products are those portions of a butchered animal which are typically unsuitable for direct marketing. For example, although certain cuts of beef, poultry or fish can be marketed to ultimate human consumers in the form in which they are removed from the animal, other less desirable portions of these animals and fish do not command a direct market and consequently must either be processed to form some desirable product or discarded.
In the poultry processing industry, the traditional, marketable portions of a chicken are generally removed from the poultry and packaged at a "processing" plant. Such portions include wings, breasts and legs. Much of the remainder of the chicken must, however, either be discarded or processed further as they are generally not otherwise marketable.
One technique for making use of poultry by-products is "rendering", i.e. the processing of the leftover poultry by-products into some other usable, marketable form. Under current practices, rendering generally includes heating the leftover by-products to a dry, cooked condition. Because poultry and other animal by-products generally contain a substantial amount of oils, these are likewise removed to form a product with both low oil and low water contents. The resulting cooked, dried, de-oiled material may then be ground to form a powder suitable for an animal feed meal and which contains a great deal of the protein and minerals of the original by-products. These proteins and minerals are the same as those in the more desirable parts of the animal and thus marketable if processed to a more desirable form. Additionally, because the original animal or poultry by-products contain bones and other mineral substances as well as meat and other protein substances, the resulting product from a rendering plant comprises a mixture of mineral by-products and protein by-products generally suitable for feeding directly to animals or poultry as part of their nutritional program.
Because of various nutritional requirements of particular animals, the mixture which results from the straight rendering of animal by-products often has a protein and mineral content somewhat different from that which is most desired by animal producers, especially those who feed their animals on a scientific basis. Accordingly, if the feed meal made from the by-products can be tailored to a particular specification, the meal will have a greater value to the customer and can command a higher price to its producer.
In the production of animal feed meals made from animal by-products, screening has been one traditional method of tailoring feed meals to particular nutritional requirements. In a screening process, particles of the feed meal produced in a rendering plant are subjected to a series of size classifications by being allowed to fall through a series of increasingly large holes so that various size particles can be collected and segregated from the original meal. In the case of most of the feed meals made from animal by-products, larger particles tend to have lower protein and higher "ash" contents, while smaller particles tend to have higher protein and lower "ash" contents. "Ash" refers to mineral-type material which remains after the cooking and grinding processes take place in the rendering plant.
Accordingly, the separation of protein-containing particles from mineral-containing particles is the most important parameter in the production of specific higher protein content components and higher mineral content components from the feed meal produced from rendered animal by-products. Although screening can classify according to size, it cannot classify by other characteristics such as density. Because a difference in density rather than a difference in particle size per se is a more typical difference between ash and protein, screen separation cannot provide a totally satisfactory method of separating the two components even though from a broader standpoint it is often adequate for less sensitive purposes.
More precise methods of separating protein from ash have generally revolved around the concept of separation of particles by these characteristic differences in density. For example, one method is gravity classification in which a typical feed meal is fed into a column of upwardly flowing air. Less dense particles are carried upward and separated by the upwardly flowing air current while those particles too dense to be affected by the air flow simply fall under the influence of gravity.
Another method uses a spiral air classifier which sets up a flow of air in a whirlpool-like flow. Less dense particles are carried along with the flow to the center of the "whirlpool" while denser particles are thrown outwardly by centrifugal force. The respective more dense and less dense particles are collected at either the perimeter or the center of the classifier. Both of these techniques are generally known as "air classification," and the change in protein content from the original mixture to the classified component is known as "protein shifting."
The aforementioned techniques have been generally satisfactory when used on vegetable by-products because the density difference between the protein components of vegetable products and the non-protein components is rather great. Accordingly, air classification of protein meals made from vegetable by-products can effectively isolate a component having double the protein content of the original mixture of by-products. Thus, air classification can increase the protein content of meals made from vegetable by-products such as cottonseeds, pea and bean powders, seed kernels and most traditionally, wheat flour.
Nevertheless, such techniques have heretofore not been used to accomplish protein shifting in meals made from animal by-products. One reason is that screen technology is most familiar to the animal rendering industry. More significantly, because the components of animal feed meals made from animal by-products do not span as wide a range of densities as do meals made from vegetable by-products, it was heretofore not recognized that classification by density could have any significant effect upon the protein content of particular feed meals made from animal by-products.
It is thus an object of the present invention to provide a method of concurrently producing feed meals made from animal by-products which have higher than average protein contents and feed meals made from animal by-products having higher than average mineral contents.
It is a further object of this invention to produce animal feed meals having a higher than average mineral content and animal feed meals having higher than average protein content.
It is a further object of this invention to provide a method of rendering animal by-products to produce a first feed meal having a higher than average mineral content and a second feed meal having a higher than average protein content.
It is another object of this invention to produce novel food meals for human or animal consumption having either higher than average protein contents or higher than average mineral contents as desired.
It is a final object of this invention to provide a method of tailoring the production and classification of food meals made from animal by-products to produce specific food meals having desired, predetermined mineral and protein contents.